Die for rolling screw threads



No. 6l8,262. Patented Jan. 24, I899.

I W. L. AMES.

DIE FOR ROLLING EW THE 8.

(Application filed 16, 1898.

(No Model.)

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UNITED STATES PATENT Orrrcn.

\VILLIAM L. AMES, OF IVOROESTER, MASSACHUSETTS, ASSIGNOR TO THE REED & PRINCE MANUFACTURING COMPANY, OF SAME PLACE;

DIE FOR ROLLING SCREW-THREADS.

SPECIFICATION forming part of Letters Patent No. 618,262, dated January 24, 1895.

Application filed May 16, 1898. Serial No. 680,891. (No model.)

To a whom it may concern:

Be it known that LWVILLIAM L. AMEs, a citizen of the United States, residing at Worcester, in the county of IVorcester and State of Massachusetts, have invented certain new and useful Improvements in Dies for Rolling Screw-Threads, of which the following is a specification.

My invention relates to dies such as are used in swaging screw-threads upon blanks by rolling and where the working faces of. the dies consist of alternate grooves and ribs, whereby a portion of the metal of the blank is forced outwardly into a spiral ridge, forming the thread.

The object of my invention is to provide dies which are easily made and which possess superior Wearing qualities.

My invention consists in an improvement in the form of the ribs on such dies and is applicable to dies for rolling straight or gimletpointed screws, particularly those known as wood-screws.

This improvement is represented in the annexed drawings, in which- Figure 1 shows a face view of the improved die. Fig. 2 is a longitudinal section of the die, taken through the bottom of one of the grooves, showing a side view of rib. Figs. 3, 4, and 5 show partial sections of the die on the lines A, B, and C, respectively, of Figs. 1 and 2 with portions of the screw as developed at these various sections.

The general form of die as used to roll woodscrewthreads consists of a steel block, in which grooves are cut of such form that the ridges or ribs left on the face of the die shall at the entering end be narrow on the working face, in order that they may be easily impressed into the metal of the blank. Proceeding toward the finishing end of the die the rib becomes wider on the face, thus broadening the groove formed in the blank until at the finishing end of the die the section of the rib corresponds with the space between the threads on the finished screw.

Dies as above described have been made by milling the grooves in the die with a cutter the angle of which corresponds with the angle of the thread of the finished screw, the narrow faces of the ribs at the entering fore stated, at the finishing portion of the die the section of the rib corresponds with the space between the threads on the finished screw.

In the operation of rolling the thread with dies as described above the ribs are forced at the beginning of the stroke to the depth desired for the finished screw-that is to say, the grooves impressed in the blank at the beginning of the stroke are not deepened during the remainder of the rolling, but only widened.

It is evident then that severe strains are put upon the ribs of the die at the place where they are weakest-via, at the sharp entering portion. In consequence of this stress excessive wear comes on this portion of the rib, with the liability of its breaking down. In order to strengthen the ribs at this point, I have in my improved die made the included angle of the working sides of the rib at the entering end of the die greater than at the opposite end, which latter must evidently agree with the angle of the groove in the finished screw.

A description of a method of making my improved die will best illustrate the gradual change in the form of rib-section from the obtuse V (a, Fig. 3) of the entering end to the more acute truncated V (b, Fig. 5) of the finishing end. A bar of steel of the form indicated by Figs. 1 and 2 is cut with a millingcutter, having a cutting angle equal to the angle of the desired thread, with parallel grooves of uniform depths and proper obliquity, depending on the diameter of the blank and the pitch of thread to be rolled, this operation completely forming the finishing end of the die. Substituting now a cutter of greater angle and beginning at what shall be the entering end of the die, the grooves are enlarged and the faces of the ribs thereby narrowed, as indicated in Fig. 1. As the cutting proceeds toward the finishing end of the die the cutter is gradually withdrawn, thus increasing the width of the face of the rib and reducing the beveled surface being cut at this operation. This withdrawal of the cutter should be so timed that without causing any abrupt change in the form of the rib it shall be entirely withdrawn from the die when the finishing portion thereof is reached.

Proceeding now to trace the operation of rolling the thread upon the blank by means of my improved die, Fig. 3 shows a partial section of the die and a portion of the blank with the grooves started upon it. It is seen that here the rib is of broad base and substantial form adapted to withstand the heavy pressures upon it. Fig. 4 shows a partial section of the die at about the middle, from end to end, and a portion of the blank with the thread as developed thus far. It is seen that the thread is changing from the blunter angle with which it was started to the more acute angle of the finished thread, this change being gradual, as before stated. In Fig. 5 is shown a part of the section taken in the finishing portion of the die with portion of finished screw.

The die as represented would roll a thread only upon a cylindrical blank. If it is desired to roll a gimlet-pointed screw, the face of the die should conform to the shape of the body of the screw on which the thread is formed; also, the grooves should become shallower on the curved portion of the die to produce the diminishing thread of the point of the screw.

The form of rib described is evidently as applicable to the pointing portions of the die as to the part rolling the body of the screw.

I claim as my invention- A die for rolling screw-threads upon blanks, the working face consisting of alternate grooves and ribs or ridges, the latter having faces which are narrow at the entering end of the die and increasing in width to the finishing part thereof, the working portion of the ribs being of V-section at the entering end of the die, the sides of the V being equally inclined to the face of the die, and the angle of the V being greater than the angle between the sides of the finished thread; the section of the Working portion of the ribs at the finishing end of the die agreeing with the corresponding space between the threads of the finished screw, intermediate portions of the ribs, between the ends of the dies, being of modified truncated V-section, the parts of the sides adjacent to the face having the same included angle as at the entering end of the die, the remaining portion of the sides having the same included angle as at the finishing portion of the die.

WM. L. AMES.

Witnesses:

H. D. REED, M. D. BRIGHAM. 

